1. Field of the Invention
The present invention relates to an MIM (Metal-Insulator-Metal) type of electric device which has a sandwich structure comprising a pair of opposing electrodes and an insulating or semiconductive medium held between the electrodes, and exhibits various electric characteristics on application of voltage to the electrodes. The present invention also relates to a process for producing the electric device, and an electronic apparatus employing the device, such as an image-displaying apparatus, an image-drawing apparatus, and an information-transferring apparatus.
2. Related Background Art
In recent years, orderly structures of organic materials have come to attract attention in connection with development and improvement of electronic functions, and molecular electronic devices employing organic molecules have come to be noticed. Consequently, Langmuir-Blodgett films (LB films) are investigated comprehensively which are considered to be one of the techniques of constructing molecular electronic devices.
The Langmuir-Blodgett film is prepared by laminating sequentially monomolecular layers of an organic compound regularly, and the thickness thereof is controllable by a molecular length. A uniform and homogeneous ultra-thin film can be formed with the Langmuir-Blodgett film. Therefore, many attempts have been made to use the Langmuir-Blodgett film for an insulator. The examples are: a tunnel junction elements of a metal/insulator/metal (MIM) structure [G. L. Larkins et al.: Thin Solid Films, vol. 99 (1983)], a luminescent element having a metal/insulator/semiconductor (MIS) structure [G. G. Roberts, et al.: Electronics Letters, vol.20, p.489 (1984)], and a switching element [N. J. Thomas et al.: Electronics Letters, vol.20, p.838 (1984)].
Heretofore, the above mentioned investigations have been conducted by using LB films of fatty acids which are relatively easy to handle. Recently, organic materials which exhibit improved heat resistance and in mechanical strength have been successfully developed. Actually, the inventors of the present invention prepared an element in a sandwich structure having an LB film of such a material held between an electroconductive material like a metal (generally called an MIM structure and an MIM type element from its construction), and observed and measured the characteristics including physical properties and electrical properties of the insulation. film, thus finding a novel switching memory phenomenon (Japanese Patent Application Laid-Open No. Sho-63-96956).
Insulating films formed by the LB method can be formed by laminating monomolecular films in the same shape as the surface of the lower electrode, and therefore does not involve the problem of nonuniformity in thickness
The lower electrode of an MIM type device has been formed hitherto by vacuum vapor deposition or sputtering. However, the metal thin film formed by such a method is polycrystalline, and inevitably shows large distribution of orientation axis of the crystal face, and the crystal plane is not simple, having many edges formed by different crystal face.
If such a device is subjected to the action of a strong electric field, the electric field tends to concentrate highly at the aforementioned edge portions, which lowers the stability and reproducibility of the device. For example, an electrode metal may migrate into an insulating layer significantly at such an edge portion. During long time of driving of the device, the device may frequently be damaged at the edge portion by dielectric breakdown or the like to considerably shorten the life of the device.